1. Field of the Invention
This invention relates in general to magnetic transducers, and more particularly to a method and apparatus for providing an aligned coil for an inductive head structure using a patterned seed layer.
2. Description of Related Art
Magnetic recording is a key and invaluable segment of the information-processing industry. While the basic principles are one hundred years old for early tape devices, and over forty years old for magnetic hard disk drives, an influx of technical innovations continues to extend the storage capacity and performance of magnetic recording products. For hard disk drives, the areal density or density of written data bits on the magnetic medium has increased by a factor of more than two million since the first disk drive was applied to data storage. Since 1991, areal density has grown by the well-known 60% compound growth rate, and this is based on corresponding improvements in heads, media, drive electronics, and mechanics.
Magnetic recording heads have been considered the most significant factor in areal-density growth. The ability of these components to both write and subsequently read magnetically recorded data from the medium at data densities well into the Gbits/in2 range gives hard disk drives the power to remain the dominant storage device for many years to come.
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating. However, when the disk rotates, air is compressed by the rotating disk adjacent the ABS causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
Prior to 1991, heads were designed with a single inductive sensor performing both reading and writing functions. The decreasing signal amplitude resulting from areal densities exceeding 500 Mbits/in2 promoted the development of magnetoresistive and giant-magnetoresistive read sensors merged with an inductive head, which now performed a write function only. While write track widths can be wider than the corresponding read widths, i.e. “write wide and read narrow”, inductive sensors must be redesigned with narrower gaps and pole geometries. At these higher data densities, pole edge effects become more significant. Coil widths and numbers of turns, all attained by advanced photolithographic techniques over large topographies, must be optimized to achieve adequate inductance focused within a very small writing area on the medium. Finally, it is a consequence of increased areal density that the media or internal data rate, i.e. the rate at which information is written and read within a disk drive, is increased.
A write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A write gap layer between the first and second pole piece layers forms a magnetic gap at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a backgap. Current conducted to the coil layer induces a magnetic field across the magnetic gap between the pole pieces. This field fringes across the magnetic gap for the purpose of writing information in tracks on moving media, such as the circular tracks on the aforementioned rotating disk or a linearly moving magnetic tape in a tape drive.
The read head includes first and second shield layers, first and second gap layers, a read sensor and first and second lead layers that are connected to the read sensor for conducting a sense current through the read sensor. The first and second gap layers are located between the first and second shield layers and the read sensor and the first and second lead layers are located between the first and second gap layers. The distance between the first and second shield layers determines the linear read density of the read head. The read sensor has first and second side edges that define a track width of the read head. The product of the linear density and the track density equals the areal density of the read head which is the bit reading capability of the read head per square inch of the magnetic media.
As mentioned above, a significant factor in achieving gigabyte densities in computers has been increasing the track density of the write head. Track density is expressed in the art as tracks per inch (TPI) which is the number of tracks that the write head can write per inch of width of a rotating disk or linearly moving magnetic tape.
The coil inductance per square turn can be reduced by decreasing the coil diameter, requiring a smaller coil pitch. However, current processing of electroplating the coil limits the coil pitch. The primary failure mode is inter-coil turn shorting to each other. The magnetic-circuit part of the inductance is dominated by the flux which fringes between the two poles and is reduced by decreasing the volume of driven magnetic material and also by increasing the separation of the two poles. But an adequate cross-section of the poles must be maintained to prevent saturation. Therefore, the easiest way to speed up a write head is to reduce the yoke length. The use of two or more coil layers facilitates these geometry changes at the expense of process complexity. If magnetic recording is to continue increasing in areal density more rapidly than semiconductor devices, a point will be reached where the lithographic resolution demands for critical dimensions of heads will exceed the capability of the conventional tooling available.
It can be seen that there is a need for a method and apparatus that provides narrower write coils to allow reduced yoke lengths and therefore greater areal densities.